1. Field of the Invention
This invention generally relates to a wheel alignment system, and more particularly, to a device for supporting a vehicle wheel in a wheel alignment system and a methodology for providing proper wheel alignment using the inventive wheel support system.
2. Description of the Prior Art
Wheel alignment machines that are used in modem vehicle assembly plants typically include a pair of support rollers at each wheel that is to be adjusted. One of the rollers is typically powered. The rollers support the weight of the vehicle while allowing the wheel to be rotated during the alignment process. Typically, support rollers are mounted on a movable carriage, however, their axes are constrained to remain parallel to each other throughout the alignment process. The wheel is rotated upon the parallel aligned rollers in order to determine the true axis of rotation of the wheel regardless of the presence of irregularities in the wheel or tire, commonly referred to as "run out".
Wheel alignment machines having rollers fixed in a parallel axes alignment have significant drawbacks associated with them. First, the constrained parallel alignment of the rollers results in undesirable lateral forces acting on the tires by the rollers, forcing the wheel out of its normal operating position, therefore leading to inaccuracies in the alignment settings.
One attempt at eliminating such undesirable lateral forces is disclosed in U.S. Pat. No. 3,187,440, wherein the magnitude of the lateral forces is measured and used to reposition the carriage until the side forces at each roller are approximately zero. The system of the '440 patent is effective, however, the feedback control system taught by the '440 patent is relatively expensive and complex, thereby, limiting the availability of such machines.
Further disadvantages associated with the prior art include the inability to repeatedly achieve accurate results in an alignment machine. Such drawbacks are especially significant in an assembly plant environment. Assembly plant alignment machines also preferably include the characteristics of having short cycle times, no attachments or physical contact with the vehicle, wheels, or the tire side walls, and no vulnerable protrusions or sensors above the floor level in the plant. None of the prior art devices provide these advantageous characteristics in an economical manner.
A further disadvantage associated with the prior art is that, in most alignment machines the vehicle is physically restrained from moving laterally by the inclusion of bumpers or additional rollers. The physical restraints are typically used to maintain stable tracking of the vehicle during the alignment process. This is necessary in order to perform the appropriate measurements and adjustments. The bumpers and/or rollers associated with the prior art are considered undesirable because they do not meet the desired characteristics of assembly plant alignment machines set forth above. Further, the use of the physical restraints implies the existence of unbalanced lateral forces at the tires.
Alignment machines that are used in service applications (i.e. dealerships or repair shops) do not require the high throughput of the assembly plant machines. Therefore, machines used in service applications are typically less expensive than the assembly plant machines, however, they are more labor intensive in order to complete the alignment process.
Further, prior art wheel alignment machines are typically very complicated in structure and in functional components. Conventional wheel alignment devices are therefore difficult to manufacture, expensive to produce, and more susceptible to malfunction.
This invention addresses the various drawbacks and shortcomings of the prior art by providing a mechanical structure that is relatively inexpensive, easy to use and effective to consistently provide precise wheel alignment measurement. This invention provides a simple and robust mechanical system able to quickly and precisely measure the angular orientation of the wheel.
One object of this invention is to provide an improved method of measurement of the angular orientation of a rotating wheel.
Another object of this invention is to rotate the wheels to be aligned while eliminating undesirable lateral forces that are otherwise introduced onto the wheel or suspension of the vehicle.
A further object of this invention is to provide stable tracking behavior of the vehicle on the alignment machine without resorting to external restraints.
In accordance with the above recited objects of this invention, it is an important aspect of this invention that the load bearing rollers are independently movable on swing arms. This feature allows for the elimination of all undesirable lateral forces at the contact points between the tire and the rollers. It is a further aspect of this invention that each wheel is contacted and supported by only two rollers, which also facilitate the function of measuring the orientation of the wheels.